1. Field of the Invention
This invention relates broadly to ophthalmic devices, and particularly to a lacrimal insert preferably in the shape of a punctum plug. More particularly, this invention relates to lacrimal inserts adapted to store and release medication.
2. State of the Art
In order to treat various conditions, drugs are administered to the eye. The most common form of drug delivery is by topical application to the eye's surface, e.g., by drops. The eye is uniquely suited to surface administration because drugs can penetrate through the cornea, rise to therapeutic concentration levels inside the eye, and exert their beneficial effects. In fact, ninety five percent of drugs delivered to the eye are currently administered through eye drops. Rarely are drugs for the eye administered orally or by injection, either because they reach the eye in too low a concentration to have the desired pharmacological effect, or because their use is complicated by significant systemic side effects.
Topical eye drops, though effective, are inefficient. When an eye drop is instilled in the eye, it overfills the conjunctival sac, the pocket between the eye and the lids, causing a substantial portion of the drop to be lost due to overflow of the lid margin onto the cheek. In addition, a substantial portion of the drop remaining on the ocular surface is washed away into the nasolacrimal duct, thereby diluting the concentration of the drug. Not only is this portion of the drug dose lost before it can cross the cornea, but this excess drug may be undesirably carried into the nose and throat where it is absorbed into the local or general circulation, sometimes leading to serious systemic side effects. The small portion of the drug in the eye drop which does penetrate the cornea results in an initial peak tissue concentration, a higher level than is required for the initial pharmacological effect. The tissue concentration then gradually decreases, such that by the time the next eye drop is due, the tissue concentration and the intended pharmacological effect may be too low.
To compound the problems described above, patients often do not use their eye drops as prescribed. Often, this poor compliance is due to an initial stinging or burning sensation caused by the eye drop. Certainly, instilling eye drops in one's own eye can be difficult, in part because of the normal reflex to protect the eye. Therefore, sometimes one or more drops miss the eye. Older patients may have additional problems instilling drops due to arthritis, unsteadiness, and decreased vision, and pediatric and psychiatric patient populations pose difficulties as well.
As a result of the above problems, there have been efforts to use a punctum plug in a manner which optimizes topical administration to take advantage of the benefits of topical administration but overcomes its drawbacks. U.S. Pat. No. 3,949,750 to Freeman describes a lacrimal insert in the shape of a punctum plug manufactured of a porous material which stores and slowly dispenses an ophthalmic medication to the eye. The Freeman plug overcomes many of the negative of topical administration, as a large proportion of the slowly dispensed medication is subject to a level rate of uptake at the eye without overflow of the conjunctival sac. If there is any drawback to the Freeman plug, it is that the dose of medication which can be stored in a solid porous plug is relatively small.
U.S. Pat. No. 6,196,993 to Cohan et al. describes a punctum plug having a reservoir within the body of the plug adapted for storing a larger quantity of medication, and a collarette having a pore in communication with the reservoir. The reservoir has a closed lower end and an upper portion open to the pore. The medication stored in the reservoir is released through the pore to the surface of the eye over time, with pore size adapted to control release rate of the medication. In one embodiment, a medication-permeable material is provided over the pore. The plug itself is shown manufactured in the patent in one piece from silicone or another material that is impermeable to the medication. However, with the reservoir being larger than the upper pore, the Cohan device cannot be manufactured as a one-piece plug. In fact, early versions of the Cohan device were manufactured with the collarette being glued or otherwise fused to a neck portion of the plug and the medication then inserted into the reservoir through the pore. This construction has serious drawbacks. Drug release or permeability is affected by locating the gluing site of the collarette to the body adjacent the pore site, as the pore may become clogged with glue or otherwise impede movement of the medication so as to affect drug release. In addition, if the permeable membrane is desired to be used over the pore, it must be placed over the collarette after filling the reservoir through the pore, which creates difficulties in product handling as the placement of such membrane may cause inadvertent premature release of medication during handling. Furthermore, any adhesive used to attach the permeable membrane to the collarette may affect the release rate of medication during implantation.